Operating states for D2D discovery

ABSTRACT

A device is configured to perform a method of device-to-device (D2D) communication in a wireless communication network in accordance with a Long Term Evolution (LTE) standard. The method includes entering an RRC-Idle state or an RRC-Connected state. The method also includes transmitting, in the RRC-Idle state or RRC-Connected state, a D2D discovery signal for receipt by at least one second device in the network. The method further includes receiving, in the RRC-Idle state or RRC-Connected state, at least one D2D discovery signal from the at least one second device in the network.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/508,795, filed on Oct. 7, 2014, (now U.S. Pat. No. 9,602,997, issuingMar. 21, 2017) which claims the benefit of U.S. Provisional ApplicationNo. 61/888,410, filed on Oct. 8, 2013, which applications are herebyincorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates generally to digital communications, andmore particularly, to a system and method for transmission and receptionof device-to-device signals in a communications system.

BACKGROUND

Systems that operate using device-to-device (D2D) standards have thepotential to provide new services, improve system throughput, and offera better user experience. The application of D2D technology is underinvestigation in 3GPP (3rd Generation Partnership Project). Potentialuse cases for D2D have been identified by 3GPP participants. Some usescases considered for the LTE (Long Term Evolution) standard areassociated with a variety of devices, including user equipment (UE),cell phones, smart phones, and network equipment, e.g., communicationscontroller, base stations, enhanced nodeB (eNB), and the like.

SUMMARY

According to one embodiment, there is provided a method ofdevice-to-device (D2D) communication in a wireless communication networkin accordance with a Long Term Evolution (LTE) standard. The methodincludes entering, by a first device, an RRC-Idle state or anRRC-Connected state; transmitting, by the first device in the RRC-Idlestate or RRC-Connected state, a D2D discovery signal for receipt by atleast one second device in the network; and receiving, by the firstdevice in the RRC-Idle state or RRC-Connected state, at least one D2Ddiscovery signal from the at least one second device in the network.

According to another embodiment, there is provided a device capable ofD2D communication in a wireless communication network in accordance witha LTE standard. The device includes at least one antenna configured totransmit and receive signals. The device also includes at least oneprocessor configured to control the device to enter an RRC-Idle state oran RRC-Connected state; transmit, while in the RRC-Idle state orRRC-Connected state, a D2D discovery signal for receipt by at least onesecond device in the network; and receive, while in the RRC-Idle stateor RRC-Connected state, at least one D2D discovery signal from the atleast one second device in the network.

According to yet another embodiment, there is provided a system for D2Dcommunication in a wireless communication network in accordance with aLTE standard. The system includes a first D2D device and a second D2Ddevice. The first D2D device is configured to enter an RRC-Idle state oran RRC-Connected state; transmit, while in the RRC-Idle state orRRC-Connected state, a D2D discovery signal for receipt by the seconddevice; and receive, while in the RRC-Idle state or RRC-Connected state,at least one D2D discovery signals from the second device.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, wherein likenumbers designate like objects, and in which:

FIG. 1 illustrates an example communication system that may be used forimplementing the devices and methods disclosed herein;

FIGS. 2A and 2B illustrate example devices that may be used forimplementing the methods and teachings disclosed herein;

FIG. 3 depicts a state diagram illustrating radio resource control (RRC)states in a LTE Version 11 system;

FIG. 4 illustrates examples of different coverage scenarios in awireless communication system;

FIG. 5 illustrates available operations in a RRC-Idle state;

FIG. 6 illustrates a modified RRC-Idle state in accordance with thisdisclosure;

FIG. 7 illustrates a modified RRC-Connected state in accordance withthis disclosure;

FIG. 8 depicts a state diagram illustrating different states ofoperation for a UE in accordance with this disclosure; and

FIGS. 9 and 10 illustrate examples of transitions between states as afunction of time for a time division duplex (TDD) configuration, inaccordance with this disclosure.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

FIGS. 1 through 10, discussed below, and the various embodiments used todescribe the principles of the present invention in this patent documentare by way of illustration only and should not be construed in any wayto limit the scope of the invention. Those skilled in the art willunderstand that the principles of the invention may be implemented inany type of suitably arranged device or system.

The following documents and standards descriptions are herebyincorporated into this disclosure as if fully set forth herein:

3GPP TR 22.803, version 12.0.0, December 2012 (hereinafter “REF1”);R1-133803, “Final Report of 3GPP TSG RAN WG1 #73 v1.0.0”, Fukuoka,Japan, May 20-24, 2013, MCC Support (hereinafter “REF2”); 3GPP TR36.300, version 11.3.0, September 2012 (hereinafter “REF3”); ArnaudMeylan, “LTE Radio Layer 2, RRC and Radio Access Network Architecture”,3GPP TSG-RAN WG2 (hereinafter “REF4”); 3GPP TR 36.304, version 11.5.0,September 2013 (hereinafter “REF5”).

FIG. 1 illustrates an example communication system 100 that may be usedfor implementing the devices and methods disclosed herein. In general,the system 100 enables multiple wireless users to transmit and receivedata and other content. The system 100 may implement one or more channelaccess methods, such as code division multiple access (CDMA), timedivision multiple access (TDMA), frequency division multiple access(FDMA), orthogonal FDMA (OFDMA), or single-carrier FDMA (SC-FDMA).

In this example, the communication system 100 includes user equipment(UE) 110 a-110 c, radio access networks (RANs) 120 a-120 b, a corenetwork 130, a public switched telephone network (PSTN) 140, theInternet 150, and other networks 160. While certain numbers of thesecomponents or elements are shown in FIG. 1, any number of thesecomponents or elements may be included in the system 100.

The UEs 110 a-110 c are configured to operate and/or communicate in thesystem 100. For example, the UEs 110 a-110 c are configured to transmitand/or receive wireless signals. Each UE 110 a-110 c represents anysuitable end user device and may include such devices (or may bereferred to) as a user equipment/device (UE), wireless transmit/receiveunit (WTRU), mobile station, fixed or mobile subscriber unit, pager,cellular telephone, personal digital assistant (PDA), smartphone,laptop, computer, touchpad, wireless sensor, or consumer electronicsdevice.

The RANs 120 a-120 b here include base stations 170 a-170 b,respectively. Each base station 170 a-170 b is configured to wirelesslyinterface with one or more of the UEs 110 a-110 c to enable access tothe core network 130, the PSTN 140, the Internet 150, and/or the othernetworks 160. For example, the base stations 170 a-170 b may include (orbe) one or more of several well-known devices, such as a basetransceiver station (BTS), a Node-B (NodeB), an evolved NodeB (eNodeB),a Home NodeB, a Home eNodeB, a site controller, an access point (AP), awireless router, a server, a switch, or any other suitable processingentity with a wired or wireless network.

In the embodiment shown in FIG. 1, the base station 170 a forms part ofthe RAN 120 a, which may include other base stations, elements, and/ordevices. Also, the base station 170 b forms part of the RAN 120 b, whichmay include other base stations, elements, and/or devices. Each basestation 170 a-170 b operates to transmit and/or receive wireless signalswithin a particular geographic region or area, sometimes referred to asa “cell.” In some embodiments, multiple-input multiple-output (MIMO)technology may be employed having multiple transceivers for each cell.

The base stations 170 a-170 b communicate with one or more of the UEs110 a-110 c over one or more air interfaces 190 using wirelesscommunication links. The air interfaces 190 may utilize any suitableradio access technology.

It is contemplated that the system 100 may use multiple channel accessfunctionality, including such schemes as described herein. In particularembodiments, the base stations 170 a-170 b and UEs 110 a-110 c areconfigured to implement LTE, LTE-A, and/or LTE-B. Additionally, inaccordance with this disclosure, one or more of the base stations 170a-170 b and UEs 110 a-110 c are configured to communicate according todevice-to-device (D2D) communication and discovery standards andprinciples. Of course, other multiple access schemes and wirelessprotocols may be utilized.

The RANs 120 a-120 b are in communication with the core network 130 toprovide the UEs 110 a-110 c with voice, data, application, Voice overInternet Protocol (VoIP), or other services. Understandably, the RANs120 a-120 b and/or the core network 130 may be in direct or indirectcommunication with one or more other RANs (not shown). The core network130 may also serve as a gateway access for other networks (such as PSTN140, Internet 150, and other networks 160). In addition, some or all ofthe UEs 110 a-110 c may include functionality for communicating withdifferent wireless networks over different wireless links usingdifferent wireless technologies and/or protocols.

Although FIG. 1 illustrates one example of a communication system,various changes may be made to FIG. 1. For example, the communicationsystem 100 could include any number of UEs, base stations, networks, orother components in any suitable configuration.

FIGS. 2A and 2B illustrate example devices that may be used forimplementing the methods and teachings disclosed herein. In particular,FIG. 2A illustrates an example UE 110, and FIG. 2B illustrates anexample base station 170. These components could be used in the system100 or in any other suitable system.

As shown in FIG. 2A, the UE 110 includes at least one processing unit200. The processing unit 200 implements various processing operations ofthe UE 110. For example, the processing unit 200 could perform signalcoding, data processing, power control, input/output processing, or anyother functionality enabling the UE 110 to operate in the system 100.The processing unit 200 also supports the methods and teachingsdescribed in more detail below. For example, the processing unit 200 isconfigured to control or support operations of the UE 110 according tothe D2D standards and principles described below. Each processing unit200 includes any suitable processing or computing device configured toperform one or more operations. Each processing unit 200 could, forexample, include a microprocessor, microcontroller, digital signalprocessor, field programmable gate array, or application specificintegrated circuit.

The UE 110 also includes at least one transceiver 202. The transceiver202 is configured to modulate data or other content for transmission byat least one antenna 204. The transceiver 202 is also configured todemodulate data or other content received by the at least one antenna204. Each transceiver 202 includes any suitable structure for generatingsignals for wireless transmission and/or processing signals receivedwirelessly. Each antenna 204 includes any suitable structure fortransmitting and/or receiving wireless signals. One or multipletransceivers 202 could be used in the UE 110, and one or multipleantennas 204 could be used in the UE 110. Although shown as a singlefunctional unit, a transceiver 202 could also be implemented using atleast one transmitter and at least one separate receiver.

The UE 110 further includes one or more input/output devices 206. Theinput/output devices 206 facilitate interaction with a user. Eachinput/output device 206 includes any suitable structure for providinginformation to or receiving information from a user, such as a speaker,microphone, keypad, keyboard, display, or touch screen.

In addition, the UE 110 includes at least one memory 208. The memory 208stores instructions and data used, generated, or collected by the UE110. For example, the memory 208 could store software or firmwareinstructions executed by the processing unit(s) 200 and data used toreduce or eliminate interference in incoming signals. Each memory 208includes any suitable volatile and/or non-volatile storage and retrievaldevice(s). Any suitable type of memory may be used, such as randomaccess memory (RAM), read only memory (ROM), hard disk, optical disc,subscriber identity module (SIM) card, memory stick, secure digital (SD)memory card, and the like.

As shown in FIG. 2B, the base station 170 includes at least oneprocessing unit 250, at least one transmitter 252, at least one receiver254, one or more antennas 256, and at least one memory 258. Theprocessing unit 250 implements various processing operations of the basestation 170, such as signal coding, data processing, power control,input/output processing, or any other functionality. The processing unit250 can also support the methods and teachings described in more detailbelow. For example, the processing unit 250 is configured to control orsupport operations of the base station 170 according to the D2Dstandards and principles described below. Each processing unit 250includes any suitable processing or computing device configured toperform one or more operations. Each processing unit 250 could, forexample, include a microprocessor, microcontroller, digital signalprocessor, field programmable gate array, or application specificintegrated circuit.

Each transmitter 252 includes any suitable structure for generatingsignals for wireless transmission to one or more UEs or other devices.Each receiver 254 includes any suitable structure for processing signalsreceived wirelessly from one or more UEs or other devices. Althoughshown as separate components, at least one transmitter 252 and at leastone receiver 254 could be combined into a transceiver. Each antenna 256includes any suitable structure for transmitting and/or receivingwireless signals. While a common antenna 256 is shown here as beingcoupled to both the transmitter 252 and the receiver 254, one or moreantennas 256 could be coupled to the transmitter(s) 252, and one or moreseparate antennas 256 could be coupled to the receiver(s) 254. Eachmemory 258 includes any suitable volatile and/or non-volatile storageand retrieval device(s).

Additional details regarding UEs 110 and base stations 170 are known tothose of skill in the art. As such, these details are omitted here forclarity.

In Version 11 of the LTE standard, a UE can have two radio resourcecontrol (RRC) states: RRC-Idle and RRC-Connected. These states weredeveloped for communications between a communication controller (e.g.,an eNB) and a UE. With the introduction of D2D discovery and D2Dcommunication, these two states may not be adequate for a UE operatingwith D2D functionality, especially when considering the variousdeployments and functions.

To illustrate, FIG. 3 depicts a state diagram of the RRC states in a LTEVersion 11 system. As shown in FIG. 3, the states are RRC-Idle andRRC-Connected. FIG. 3 also shows that the RRC-Connected state has twosub-states: Dormant and Active. For the sake of brevity, the “RRC-Idlestate” is also sometimes referred to herein as the “idle state”.Likewise, the “RRC-Connected state” is also sometimes referred to hereinas the “connected state”.

For D2D, two functions are envisioned: Communication and Discovery.These functions are now defined.

Communication: When performing a Communication function, a UE directlycommunicates with other UEs without the communication data passingthrough the eNB. A UE in D2D communication with another device is notprecluded from performing cellular communication (i.e., exchanging datawith another entity through the communications controller).

Discovery: When performing discovery, a UE both can discover and isdiscoverable. That is, a UE can attempt to discover neighboring UEs byreceiving discovery signals, and can transmit discovery signals forother UEs to discover it.

In some environments, a UE may be in-coverage (IC) or out-of-coverage(OOC). When the UE is IC (i.e., in-network coverage), the UE canestablish a link with an eNB. When the UE is OOC (i.e., out-of-networkcoverage), the UE cannot establish a link with an eNB. Typically, if aUE can receive synchronization signals, such as the primarysynchronization signal (PSS), secondary synchronization signal (SSS),master information block (MIB), and system information block (SIB), theUE can be considered in-coverage (IC). Conversely, if the UE cannotreceive such information, it is out-of-coverage (OOC).

To illustrate, FIG. 4 depicts examples of different coverage scenariosin a wireless communication system. As shown in FIG. 4, the system 400includes an eNB 410 and a plurality of devices represented by UEs 420a-420 d. In certain embodiments, the eNB 410 may represent one or moreof the base stations 170 a-170 b of FIG. 1, and the UEs 420 a-420 d mayrepresent one or more of the UEs 110 a-110 c of FIG. 1. The eNB 410controls communications within a coverage area 430. In the system 400,the UEs 420 a-420 b are in-network coverage, while the UE 420 d may beconsidered out-of-network coverage. The UE 420 c may be in partialnetwork coverage due to its proximity to the coverage area 430 of theeNB 410.

During LTE standardization discussions, D2D discovery was categorized bytwo types, as indicated by the following text from REF2:

“At least the following two types of discovery procedure are defined forthe purpose of terminology definition for use in furtherdiscussions/studies (note that these definitions are intended only toaid clarity and not to limit the scope of the study):

-   -   Type 1: a discovery procedure where resources for discovery        signal transmission are allocated on a non UE specific basis        -   Note: Resources can be for all UEs or group of UEs    -   Type 2: a discovery procedure where resources for discovery        signal transmission are allocated on a per UE specific basis        -   Type 2A: Resources are allocated for each specific            transmission instance of discovery signals        -   Type 2B: Resources are semi-persistently allocated for            discovery signal transmission.”

Based on the current LTE definitions, UEs are either in RRC-Connected orRRC-Idle state with respect to a network. When a UE operates in theRRC-Idle state, the only signal the UE can transmit is the physicalrandom access channel (PRACH). For all other transmissions, the UEenters the RRC-Connected state. Thus, under LTE Version 12, it isenvisioned that devices participating in communication with each otherare operating in the RRC-Connected state. However, for D2D discoverysignal transmission, operating in RRC-Connected state may not befeasible due to the overhead associated with establishing an RRCconnection. Furthermore, OOC devices (i.e., devices that areout-of-network coverage) cannot enter the RRC connected state sincethere is no network to connect to.

The functionalities of the RRC-Idle and RRC-Connected states describedin REF5 are shown below:

RRC-Idle:

-   -   PLMN selection;    -   DRX configured by NAS;    -   Broadcast of system information;    -   Paging;    -   Cell re-selection mobility;    -   The UE shall have been allocated an id which uniquely identifies        the UE in a tracking area;    -   No RRC context stored in the eNB.    -   RRC-Connected:    -   UE has an E-UTRAN-RRC connection;    -   UE has context in E-UTRAN;    -   E-UTRAN knows the cell which the UE belongs to;    -   Network can transmit and/or receive data to/from UE;    -   Network controlled mobility (handover and inter-RAT cell change        order to GERAN with NACC);    -   Neighbor cell measurements;    -   At PDCP/RLC/MAC level:        -   UE can transmit and/or receive data to/from network;        -   UE monitors control signaling channel for shared data            channel to see if any transmission over the shared data            channel has been allocated to the UE;        -   UE also reports channel quality information and feedback            information to eNB;        -   DRX period can be configured according to UE activity level            for UE power saving and efficient resource utilization. This            is under control of the eNB.

FIG. 5 illustrates available operations in the RRC-Idle state, asdescribed in REF5.

For D2D communication, not all functions available in the RRC-Connectedstate may be needed, especially for out-of-network coverage. However,there is a need for a UE to communicate using D2D functionality whileoutside network coverage and to use limited resources while in networkcoverage.

With the introduction of D2D, the current mapping of the idle state andconnected state can be insufficient. The requirement that devices be inthe connected state for the transmission of discovery signals canincrease system overhead (e.g., increased messaging between the deviceand the communications controller) and can consume system resources(e.g., memory, ports). In addition, a device may be subject to increasedpower consumption due to the requirements of the connected state.Furthermore, the notion of the connected state is not applicable todevices out-of-network coverage.

To address the limitations of the current two states, RRC-Idle andRRC-Connected, embodiments of this disclosure provide a new state,D2D-Connected state, configured to support D2D communications and D2Ddiscovery. In other embodiments of this disclosure, the existing states,RRC-Idle and RRC-Connected, are modified to support D2D discovery andD2D communication. It will be understood that combinations of two ormore of the disclosed embodiments can be used for D2D.

In an embodiment, the available functionalities of the RRC-Idle stateare modified so that a UE can transmit D2D discovery signals. FIG. 6illustrates the modified RRC-Idle state according to this embodiment. Asshown in FIG. 6, the available functionalities of the modified RRC-Idlestate include two new features, indicated at reference number 600:

“The UE shall have been allocated a D2D ID”; and

“Transmission and monitoring of discovery signals”.

In accordance with the modified RRC-Idle state, a UE is allocated a D2Didentifier (D2D ID). The D2D ID can be a network assigned value; forexample, the D2D ID can be provided to the UE during a registrationprocess. However, it will be understood that the D2D ID can be allocatedto the UE in any other suitable manner. The modified RRC-Idle state andthe associated D2D ID enables the UE to perform D2D discovery while inthe RRC-Idle state.

In another embodiment, the available functionalities of theRRC-Connected state are modified so that a UE can perform discovery.FIG. 7 illustrates the modified RRC-Connected state according to thisembodiment. As shown in FIG. 7, the available functionalities of themodified RRC-Connected state include one new feature, indicated atreference number 700:

“Transmission and monitoring of discovery signals”.

In accordance with the modified RRC-Connected state, the UE is able toperform D2D discovery while engaging in cellular communications (i.e.,transmissions between the UE and a communications controller, such as aneNB) or engaging in D2D communications. A D2D ID can be assigned to theUE in the RRC-Connected state.

In another embodiment, a new state, “D2D-Connected”, is introduced. Inthe D2D-Connected state, the UE can transmit D2D signals without beingin the RRC-Connected state. As in the modified RRC-Idle andRRC-Connected states, a UE in the D2D-Connected can be assigned a D2DID. A list of possible actions and functionalities associated with theD2D-Connected state is provided below. In some embodiments, theD2D-Connected state can be a subset of the RRC-Idle state, theRRC-Connected state, or both.

D2D-Connected:

-   -   The UE shall have been allocated a D2D ID;    -   Monitoring of discovery configuration SIB (for Type 1 discovery)        OR the UE has previously received a discovery resource        allocation and parameters (for Type 2 discovery);    -   Coarse synchronization with the master UE or eNB;    -   Transmission and monitoring of discovery signals per the        resources allocated for discovery and the discovery parameters.

FIG. 8 depicts a state diagram illustrating the different states ofoperation for a UE in accordance with this disclosure. As shown in FIG.8, the UE may operate in any of RRC-Connected state 801, the RRC-Idlestate 802, or the D2D-Connected state 803. As indicated by the arrows, aUE operating in the RRC-Idle state 802 can transition directly to eitherthe RRC-Connected state 801 or the D2D-Connected state 803. A UEoperating in the RRC-Connected state 801 can transition directly to theRRC-Idle state 802; to transition from the RRC-Connected state 801 tothe D2D-Connected state 803, the UE first transitions to the RRC-Idlestate 802, and then to the D2D-Connected state 803. Similarly, a UEoperating in the D2D-Connected state 803 can transition directly to theRRC-Idle state 802; to transition from the D2D-Connected state 803 tothe RRC-Connected state 801, the UE first transitions to the RRC-Idlestate 802, and then to the RRC-Connected state 801.

In another embodiment, the operation of the RRC-Idle state and theD2D-Connected state are combined. For example, in a typical, non-D2Denvironment, when a UE operates in the RRC-Idle state, the UE canreceive broadcast information, such as discovery resource allocation,from its master controller (e.g., an eNB for in-coverage or a master UEfor out-of-coverage deployments). The UE also obtains coarsetime-frequency synchronization. In contrast, in a D2D system, a UE inthe RRC-Idle state can enter a D2D-Connected state during discoveryinstances. In the D2D-Connected state, the UE can transmit or receivediscovery signals on discovery resources. Afterwards, the UE can returnto the RRC-Idle state.

FIG. 9 illustrates an example of this transition between states as afunction of time for a time division duplex (TDD) configuration, inaccordance with this disclosure. As shown in FIG. 9, a UE in an idlestate (e.g., RRC-Idle state) can transition to a discovery state (e.g.,D2D-Connected state) in order to transmit or receive discovery signalson discovery resources, then transition back to the idle state.

In some embodiments, there may be some restrictions on operations. Inone example, during the D2D-Connected state, only discovery isperformed, and none of the functionalities of the RRC-Idle state (e.g.,cell reselection, reception of paging signal) is repeated. If discoveryis performed on uplink resources (e.g., resources for transmission ofsignals from the UE to a communications controller), such restrictionson downlink (e.g., transmissions from a communications controller) maynot be needed. For example, in a frequency division duplex (FDD)configuration, the UE downlink can be in the RRC-Idle state while the UEuplink is in the D2D-Connected state.

In another embodiment, a UE can perform discovery transmission/receptionon discovery resources while operating in the RRC-connected state. Thatis, a UE in the RRC-Connected state can enter a D2D-Connected state totransmit or receive discovery signals on discovery resources, thenreturn to the RRC-Connected state. FIG. 10 illustrates an exampledescription of this transition between states for a TDD configuration.As shown in FIG. 10, a UE in a RRC-Connected state can transition to adiscovery state (e.g., D2D-Connected state) to perform discovery, thentransition back to the RRC-Connected state.

In some embodiments, such as the embodiments shown in FIGS. 9 and 10,the transition between states can occur on time boundaries, such as thestart of a subframe. For example, in LTE, a subframe represents 1 msec,and a frame, which consists of 10 subframes, is 10 msec. Each subframeincludes 2 slots, each 0.5 msec in duration. In systems with a normalcyclic prefix, there can be 7 symbols per slot. In a D2D system, thetransition between states can occur at the start of a subframe, a frame,a slot, or a symbol.

In some embodiments, in the event that the UE leaves the RRC-Connectedstate (e.g., due to a lost connection), the UE should enter the RRC-Idlestate first, even if the current subframe is designated as a discoverysubframe.

In some embodiments, some or all of the functions or processes of theone or more of the devices are implemented or supported by a computerprogram that is formed from computer readable program code and that isembodied in a computer readable medium. The phrase “computer readableprogram code” includes any type of computer code, including source code,object code, and executable code. The phrase “computer readable medium”includes any type of medium capable of being accessed by a computer,such as read only memory (ROM), random access memory (RAM), a hard diskdrive, a compact disc (CD), a digital video disc (DVD), or any othertype of memory.

It may be advantageous to set forth definitions of certain words andphrases used throughout this patent document. The terms “include” and“comprise,” as well as derivatives thereof, mean inclusion withoutlimitation. The term “or” is inclusive, meaning and/or. The phrases“associated with” and “associated therewith,” as well as derivativesthereof, mean to include, be included within, interconnect with,contain, be contained within, connect to or with, couple to or with, becommunicable with, cooperate with, interleave, juxtapose, be proximateto, be bound to or with, have, have a property of, or the like.

While this disclosure has described certain embodiments and generallyassociated methods, alterations and permutations of these embodimentsand methods will be apparent to those skilled in the art. Accordingly,the above description of example embodiments does not define orconstrain this disclosure. Other changes, substitutions, and alterationsare also possible without departing from the spirit and scope of thisdisclosure, as defined by the following claims.

What is claimed is:
 1. A method of device-to-device (D2D) communicationin a wireless communication network in accordance with a Long TermEvolution (LTE) standard, the method comprising: receiving, by a firstdevice from the network, an allocation of a D2D identifier (ID) for D2Ddiscovery operation; entering, by first device, a radio resourcecontrol-idle (RRC-Idle) state or a radio resource control-connected(RRC-Connected) state, in a cell of the network in which the firstdevice is located; transmitting, by the first device in the RRC-Idlestate or the RRC- Connected state, on a first set of discoveryresources, without requesting authorization from an enhanced node B(eNB) of the cell, a first D2D discovery signal for reception by asecond device in the RRC-Idle state or the RRC-Connected state in thenetwork; and receiving, by the first device in the RRC-Idle state or theRRC-Connected state, on a second set of discovery resources, a secondD2D discovery signal transmitted by a third device in the RRC-Idle stateor the RRC-Connected state in the network, the first and second sets ofdiscovery resources being allocated on a non-device-specific basis. 2.The method of claim 1, the transmitting the D2D discovery signalcomprising: transitioning to a D2D-Connected state to transmit the D2Ddiscovery signal; and transitioning back to the RRC-Idle state or theRRC-Connected state after transmitting the D2D discovery signal.
 3. Themethod of claim 2, further comprising transitioning between the statesat an occurrence of a frame boundary or a subframe boundary.
 4. Themethod of claim 1, further comprising: entering, by the first device, aD2D-Connected state; and performing D2D communication with the seconddevice while in the D2D-Connected state.
 5. The method of claim 1, theentering the RRC-Idle state or the RRC-Connected state comprisingentering the RRC-Connected state, and the transmitting the D2D discoverysignal comprising transmitting, by the first device, the D2D discoverysignal while in the RRC-Connected state and while engaged in cellularcommunication with a fourth device.
 6. A first device capable ofdevice-to-device (D2D) communication in a wireless communication networkin accordance with a Long Term Evolution (LTE) standard, the firstdevice comprising: a non-transitory memory storage comprisinginstructions; and one or more processors in communication with thememory storage, wherein the one or more processors execute theinstructions to: receive, from the network, an allocation of a D2Didentifier (ID) for D2D discovery operation; enter a radio resourcecontrol-idle (RRC-Idle) state or a radio resource control-connected(RRC-Connected) state, in a cell of the network in which the firstdevice is located; transmit, while in the RRC-Idle state or theRRC-Connected state, on a first set of discovery resources, withoutrequesting authorization from an enhanced node B (eNB) of the cell, afirst D2D discovery signal for reception by a second device in theRRC-Idle state or the RRC-Connected state in the network; and receive,while in the RRC-Idle state or the RRC-Connected state, on a second setof discovery resources, a second D2D discovery signal transmitted by athird device in the RRC-Idle state or the RRC-Connected state in thenetwork, the first and second sets of discovery resources beingallocated on a non-device-specific basis.
 7. The first device of claim6, wherein the one or more processors executing the instructions totransmit the D2D discovery signal comprises the one or more processorsexecuting the instructions to: transition to a D2D-Connected state totransmit the D2D discovery signal; and transition back to the RRC-Idlestate or the RRC-Connected state after transmitting the D2D discoverysignal.
 8. The first device of claim 7, wherein the one or moreprocessors execute the instructions to transition between the states atan occurrence of a frame boundary or a subframe boundary.
 9. The firstdevice of claim 6, wherein the one or more processors execute theinstructions to: enter a D2D-Connected state; and perform D2Dcommunication with the second device while in the D2D-Connected state.10. The first device of claim 6, wherein the one or more processorsexecuting the instructions to enter the RRC-Idle state or theRRC-Connected state comprises the one or more processors executing theinstructions to enter the RRC-Connected state, and wherein the one ormore processors executing the instructions to transmit the D2D discoverysignal comprises the one or more processors executing the instructionsto transmit the D2D discovery signal while in the RRC-Connected stateand while engaged in cellular communication with a fourth device.
 11. Asystem for device-to-device (D2D) communication in a wirelesscommunication network in accordance with a Long Term Evolution (LTE)standard, the system comprising: a first D2D device in the network; asecond D2D device in the network, and a third D2D device in the network,wherein the first D2D device is configured to: receive, from thenetwork, an allocation of a D2D identifier (ID) for D2D discoveryoperation; enter a radio resource control-idle (RRC-Idle)state or aradio resource control-connected (RRC-Connected) state, in a cell of thenetwork in which the first D2D device is located; transmit, while in theRRC-Idle state or the RRC-Connected state, on a first set of discoveryresources, without requesting authorization from an enhanced node B(eNB) of the cell, a first D2D discovery signal for reception by thesecond D2D device in the RRC-Idle state or the RRC-Connected state; andreceive, while in the RRC-Idle state or the RRC-Connected state, on asecond set of discovery resources, a second discovery signal transmittedby the third D2D device in the RRC-Idle state or the RRC-Connectedstate, the first and second sets of discovery resources being allocatedon a non-device-specific basis.
 12. The system of claim 11, wherein thefirst D2D device configured to transmit the first D2D discovery signalcomprises the first D2D device configured to: transition to aD2D-Connected state to transmit the first D2D discovery signal; andtransition back to the RRC-Idle state or the RRC-Connected state aftertransmitting the first D2D discovery signal.
 13. The system of claim 12,wherein the first D2D device is configured to transition between thestates at an occurrence of a frame boundary or a subframe boundary. 14.The system of claim 11, wherein the first D2D device is configured to:enter a D2D-Connected state; and perform D2D communication with thesecond D2D device while in the D2D-Connected state.
 15. The system ofclaim 11, wherein the first D2D device configured to enter the RRC-Idlestate or the RRC-Connected state comprises the first D2D deviceconfigured to enter the RRC-Connected state, and wherein the first D2Ddevice configured to transmit the D2D discovery signal comprises thefirst D2D device configured to transmit the D2D discovery signal whilein the RRC-Connected state and while engaged in cellular communicationwith a fourth device.